Wind is a powerful renewable energy source that civilizations have harnessed to varying degrees for several thousand years. Historians accredit ancient Mesopotamia and Egypt as giving rise to sail-based propulsion systems for boats, while most accounts accredit ancient Persia as having developed and implemented windmills in 500 to 900 AD. In around 1390, the Dutch began to refine the windmill, eventually implementing thousands for various applications such as irrigation, land drainage, grain-grinding, saw-milling and the processing of commodities.
With the current awareness of global warming and the human impact upon the environment, there is an increasing shift towards greener, ecologically-friendly technologies. While fossil fuel-fired and nuclear powerplants have been standard methods of power generation for the last century, alternative methods for power generation, particularly from renewable energy sources such as the sun and wind have been attracting increasing attention from industry, governments and the general public.
Modern windmills for power generation are growing in popularity, with wind farms being established in many countries around the world. Modern windmills come in a variety of sizes and configurations, but many associate windmills with the large horizontal wind turbines used for large scale energy generation. These large turbines, generating megawatts of electricity, can stand as tall as 90 meters, with generally three equidistantly spaced blades measuring upwards of 30 meters each. Most large turbines require a transmission, which contributes to their often noted and criticized noise characteristics.
At the same time, there is growing interest for smaller turbine units that are better suited to farm and residential application. Unfortunately, these smaller units are subject to less than optimal wind characteristics as these units are generally located closer to the ground for aesthetic and practical reasons. As such, there is a need for smaller turbine units having wind capturing characteristics that are suited for the conditions under which these smaller turbine units are operated.
While it would seem that a scaled-down version of the common horizontal wind turbine would be suitable for smaller applications, three blades on one rotor can be difficult to balance on rotation, particularly at the higher rates of rotation common on smaller wind turbines. The combination of irregular rotary motion of the wind blades generally results in vibrations from the wind blades and low frequency sounds reverberating from the wind turbine assembly. Numerous studies suggest that vibrations and low frequency sounds emitted by wind turbines cause latent nervous conditions on humans and farm animals.
More recently, multi-rotor wind turbines have been proposed wherein multiple rotors are used to capture and translate wind energy into electricity. While effective at capturing wind, particularly in areas of increased turbulence, such as ground level applications, problems arise in maintaining the rotors balance given the totality of blades present. As such, there clearly exists a need for a rotor mounting system that addresses the shortcomings of current multi-rotor wind turbines.